LITHOSTRATIGRAPHIC MAPPING IN THE FARGO-MOORHEAD AREA—WEST-CENTRAL MINNESOTA AND SOUTHEASTERN NORTH DAKOTA

The Minnesota Geological Survey and North Dakota Geological Survey have compiled and reinterpreted existing studies in the Fargo-Moorhead area to develop an interstate interpretation of the Quaternary stratigraphy and surface geology. This work was combined with regional cross sections in ArcView and used to develop a three-dimensional model of the geology of the region.

Previous studies of the Quaternary stratigraphy in the area have been local in scope due to agency and project-specific requirements. This study combined available data and reinterpreted them in a regional, interstate context using computer-assisted techniques. The project database contains information on 3,650 samples from North Dakota and Minnesota Quaternary databases and represents samples collected from 112 borehole and rotary-sonic core sites (2,000 samples), and 1,037 outcrops and soil-probe sites (1,650 samples). Computer-assisted interpretation techniques defined 23 lithostratigraphic units. Eighteen units were known from previous studies in the project area, one unit was known from previous studies east of the Fargo-Moorhead area, and four units were older tills that are poorly represented in the study area. Stratigraphic correlations were developed using ArcView-generated water-well cross sections and geologic control developed by this study.

A surficial lithologic map was compiled from available geologic maps of the North Dakota and Minnesota portions of the study area. Map units were developed that allowed the geologic maps from the various sources to be combined and interpreted; they describe sediment type, interpreted age, and interpreted origin of the surface sediment. Areas of surface exposure of Quaternary stratigraphic units were defined and combined with the lithologic map to produce the Fargo-Moorhead lithostratigraphic map.

This work was done under contract to the U.S. Department of the Interior, Bureau of Reclamation in support of their Red River Valley Water Supply Project and represents an important cooperative effort between North Dakota and Minnesota. It illustrates the fundamental necessity of interstate cooperation between the agencies responsible for the development of an understanding of the geology of the Red River Valley and associated environmental and water related problems in the area.